In recent years, resin materials (e.g. olefin-based resins, matrix resins of fiber reinforced plastic (FRP), and the like) have been used for automobile bodies in place of steel plates from the perspective of reducing weight.
Use of one-component moisture-curable urethane composition, as a direct glazing adhesive (hereinafter, also abbreviated as “DG adhesive”) used to adhere such a body and window glass of an automobile, has been known.
For example, Japanese Unexamined Patent Application Publication No. 2006-176664A describes “a one-component moisture-curable urethane composition including, per 100 parts by mass of a urethane prepolymer, from 2 to 32 parts by mass of a carbon black (A) having a particle diameter of 20 to 25 nm, and from 8 to 38 parts by mass of a carbon black (B) having a particle diameter of 26 to 30 nm”.
Furthermore, Japanese Unexamined Patent Application Publication No. 2014-502644A discloses “in a two-component polyurethane adhesive agent system containing a resin component A and a separately packed curing agent B, the resin component A contains a mixture of monomeric polyisocyanates of aromatic polyisocyanate and aliphatic polyisocyanate (Claim 3). Examples of such an aliphatic polyisocyanate include trimerized hexane-1,6-diisocyanate (paragraph 0021)”.
Conventionally known one-component moisture-curable urethane composition, such as those described in Japanese Unexamined Patent Application Publication No. 2006-176664A and the like, had a problem of slow curing speed.
When the inventors of the present technology changed the specification thereof to two-component composition using a main agent and a curing agent from the perspective of enhancing the curing speed, it was found that, as the curing speed increases, adhesion to a base material (especially, a base material formed from an olefin-based resin) may be deteriorated and, depending on the structure of the urethane prepolymer, heat resistance also may be deteriorated.
Furthermore, when the present inventors produced a two-component urethane-based adhesive composition containing a trimerized hexane-1,6-diisocyanate (specifically, an isocyanurate of hexamethylene diisocyanate) as a compound having an isocyanurate ring using Japanese Unexamined Patent Application Publication No. 2014-502644A as a reference, it was found that the viscosity may be increased excessively, thereby causing deterioration in workability.